Ethylene copolymers are used for various applications by melt processing with various methods. The ethylene copolymers are usually required to have high melt tension suitable for melt molding. For example, for securing the stability of blown tubes during blown film extrusion process, for preventing sagging and tearing and for getting a uniform thickness distribution during blow molding process, and for preventing the decreases of film width (neck in) of molten resin during cast film process and extrusion-coating process, ethylene copolymers having high melt tension are required.
For producing ethylene polymers having high melt tension and excellent processability, for example, Japanese Patent Application No. 09-328520A describes an ethylene copolymer of which density and melt flow rate (MFR) are from 0.880 to 0.980 g/cm3 and from 0.01 to 100 g/10 min. respectively, of which melt tension and MFR satisfy a specific relationship, of which fluidity index and MFR satisfy a specific relationship, and of which swell ratio is higher than 1.40. And also it describes a specific method for extruding the ethylene copolymer, a method for producing granulated pellets by using a conical tapered twin screw extruding machine manufactured by HAAKE and melt extruding at 180° C.
However, further improvement has been desired for the transparency of the molded articles such as films made of the ethylene copolymer described in the above publication.